Question : Laptop fan high RPM

I have an older IBM ThinkPad T43 Intel Pentium M CPU 2GHz, 2GB RAM.

The problem is the fan start working on very high RPM almost all the time.  Sometimes it goes to low-high-low-high mode every second.  But most of the time its just very high RPM.  
What could be the problem?  Is the CPU overheating and needs to be cooled constrantly?  Or the voltage regulator's problem?
Any advice?
Oh, I also noticed the system got slower then before.
Thanks!

Answer : Laptop fan high RPM

The T4x series were somewhat noted for noisy fans. Check your power manager (IBM or Windows or both) and make sure your CPU is set for adaptive (managed) mode. Your CPU should be running about 600 or 800 Mhz most of the time and not flat out. Also install a temperature meter (Mobile Meter). When the CPU goes over about 37 C the fan will go on high. Once cooled down and adaptive, the fan should spin down. Any load will cause it to speed up. Check by putting the laptop on a hard surface (for air flow) and let it idle for 30 minutes.

If after all, it will not spin down, there may be a hardware problem. Also try updating the BIOS before concluding there is a hardware problem.  ... Thinkpads_User